Recently, due to the high integration and miniaturization of semiconductor devices, and complexity of the manufacturing process thereof, various defects that cause problems in the operations of the devices have been generated. Such defects serve as the cause for reduction of performance and yield of the semiconductor device, and thus the semiconductor device manufacturing companies are putting a lot of efforts into addressing this problem.
In general, the defects are known to be caused by a mask misalignment, contaminants, voids, and non-uniformity of an impurity concentration inside the semiconductor devices, etc. The types of defects include open/short of a metal interconnection, increased local resistance, abnormal contact resistance, micro-plasma leakage of an oxide layer, oxide layer breakdown, and device latch-up, etc.
Recently, due to the fine pattern and high integration of the semiconductor devices, the yield is significantly decreased by small sizes (for example, about 1 μm or less) of internal defects, process defects, or pattern defects. Thus, the importance of the defect analysis has become significant in increasing the productivity. It is because that the production costs can be saved from the increased productivity.
When the defects were generated in the semiconductor device, the method of determining the cause of the defects is as follows. After the manufacturing process is completed, the electrical defects of the device are determined and then the positions of the defects are analyzed with accuracy of within several micro-meters using a variety of non-destructive methods (thermal emission microscopy, photon emission microscopy, scanning acoustic microscopy, etc.). Then, the semiconductor wafer is cut at a point where a defect is assumed to exist using a focused ion beam (FIB), and the cut section is enlarged and observed through a scanning electron microscope (SEM). The causes of the defects can also be analyzed using a composition analysis equipment.
Many types of defects such as a metal short, resistive open, micro-plasma leakage, oxide layer breakdown, and device latch-up in the semiconductor device cause a hot spot.
Therefore, semiconductor manufacturing companies use a semiconductor defect inspection technique such as infrared thermal emission technique. The technique detects infrared thermal emission by the hot spot generated from the semiconductor defects using a mid-infrared (wavelength in a range of 3 μm to 5 μm) microscope. However, in infrared thermal emission technique, the physical limit of spatial resolution is about 3 μm due to the optical diffraction limit, and thus, there is a limit on the accuracy of defect position tracking in the highly integrated and fine patterned semiconductor device.
With the rapid progress of the fine pattering and increase of the degree of integration by the development of the semiconductor manufacturing process techniques, the semiconductor manufacturing companies have required defect analyzing tools of the higher spatial resolution than that of the commercialized defect inspection equipment.
A new method was reported in various ways. It is a thermoreflectance microscopy technique. In this technique, ultraviolet or visible light is illuminated onto the sample through the optical microscope, the distribution of reflectivity change due to the hot spot of the sample is measured by a phase-lock thermal reflection method, and then the heat distribution of the sample is derived from the measured result. Heat distribution measurement/analysis techniques in the semiconductor devices using the new method have been reported.
For example, U.S. Pat. No. 7,173,245 “Submicron thermal imaging method and enhanced resolution (super-resolved) ac-coupled imaging for thermal inspection of integrated circuits” discloses an invention which relates to the thermoreflectance microscope based system and the semiconductor device thermal analysis.
Further, U.S. Pat. No. 7,429,735 “Methods of thermoreflectance thermography” discloses an invention for improving the spatial resolution of the thermal images by using a confocal microscope principle in addition to the thermoreflectance microscope principle.
Further, US Pat. No. US2009/0084659 “High performance CCD-based thermoreflectance imaging using stochastic resonance” discloses an invention for improving the thermal resolution by adding the stochastic resonance (digital signal processing) principle to the thermoreflectance microscope.
However, there are still many problems in which these characteristic measurement methods have been little utilized for the defect analysis of the semiconductor device so far. Some methods may have to cut the sample, and some methods need an excessive amount of time, etc. When the semiconductor device is analyzed, the sample wafer may get damaged in wafer cutting process, which may cause the defect analysis impossible.
Furthermore, since various types of materials such as a metal, a dielectric, a semiconductor material, and the like are exposed on the surface of the semiconductor device, it may be difficult to effectively measure the heat distribution using the common thermoreflectance microscope.